Motion compensating apparatus

ABSTRACT

Compensating apparatus connected between a travelling block of a well bore rig mounted on a vessel float in a body of water and a hook from which a running string is supportable, the compensating apparatus including a pair of elongate cylinders straddling and connected to the travelling block and a pair of companion piston rods connected to and straddling the hook and secured to pistons relatively longitudinally shiftable in the cylinders, liquid under pressure being maintained in the cylinders under the pistons to support a substantial portion of the weight of the running string suspended from the hook. The compensating apparatus can be rendered inoperative when desired. Shock absorbers retard sudden upward movement and retraction of the compensating apparatus in the event of sudden release or diminution of the load on the apparatus, as might result from failure of the running string.

United States Patent [191 Hanes et al.

1 1 MOTION COMPENSATING APPARATUS [75] Inventors: .Tames ET Planes, Veritiirai Edward Larralde, Santa Barbara, both of Calif.

[73] Assignee: Vetco Offshore Industries, Inc.,

Ventura, Calif.

22 Filed: Sepl.4, 1970 [21] Appl.No.: 69,759

[52] U.S. Cl. ..175/5, 175/27, 254/172 [51] Int. Cl. ..E2lb 7/12 [58]Field of Search ..175/5, 27, 7, 85; 254/172, 254/135, 129, 130

[56] References Cited UNITED STATES PATENTS 3,460,638 8/1969 Millsapps..175/85 3,151,686 10/1964 Kammerer ..175/5 3,158,208 11/1964 Kammerer..175/5 X 3,208,728 9/1965 Parks ..175/5 X 3,390,654 7/1968 Bromell..175/5 X 3,369,793 2/1968 Boldrick ..254/30 3,469,820 9/1969 Horton..254/172 [4 1 Feb. 6, 1973 Primary ExaminerRobert L. Wolfe AssistantExaminer Richard E. Favreau Att0rney-Bernard Kriegel [57] ABSTRACTCompensating apparatus connected between a travelling block of a wellbore rig mounted on a vessel float in a body of water and a hook fromwhich a running string is supportable, the compensating apparatusincluding a pair of elongate cylinders straddling and connected to thetravelling block and a pair of companion piston rods connected to andstraddling the hook and secured to pistons relatively longitudinallyshiftable in the cylinders, liquid under pressure being maintained inthe cylinders under the pistons to support a substantial portion of theweight of the running string suspended from the hook. The compensatingapparatus can be rendered inoperative when desired. Shock absorbersretard sudden upward move ment and retraction of the compensatingapparatus in the event of sudden release or diminution of the load onthe apparatus, as might result from failure of th running string.

24 Claims, 5 Drawing Figures PATENTEDFEB 6 1975 saw 1 or 3 MOTIONCOMPENSATING APPARATUS The present invention relates to apparatus forcontrolling the stress in a running string, and more particularly toapparatus used on or in connection with a floating vessel formaintaining the strain in a running string, such as a pipe string,substantially constant while being used in the performance of diversefunctions in a subaqueous well bore, such asdrilling and completionoperations therein, despite vertical movement of the vessel while suchoperations are being performed.

In the normal operation of drilling a well bore on land, or from adrilling platform supported in a fixed position from the ocean floor,the weight on the drilling bit is equal to the total weight of thedrilling string less the weight of the drill pipe carried by thedrawworks. Usually, the weight imposed on the bit is equal to the weightof the drill collar sections connected to the lower end of the drillpipe. In drilling a sub-aqueous well bore from a floating vessel, theheaving of the vessel under tide, wind and wave conditions introducesproblems of maintaining the drilling weight on the bit at the desiredvalue. At the present time, compensation for vessel heaving is generallyaccomplished through use of a slidable spline connection in the drillstring above the drill collars. Although such slidable spline connectionis widely used, it presents many difficulties, the principal one beingthe requirement that ittransmit torque. When subjected to high torque,sufficient friction is developed in the spline as to render the freesliding of the joint ineffective. Moreover, such slidable splineconnections have comparatively low torsional strength, resulting intheir failure with attendant very high fishing costs. At times, theresult of the failure has been the abandonment ofa costly well.

Motion compensating devices have been proposed for overcoming theaforenoted difficulty, in which the drill string is supportedhydraulically by interposing a compensating apparatus between thetravelling block and hook of the usual drilling apparatus employed indrilling the well bore. Such types of apparatus, and similar apparatus,are illustrated in US. Pat. Nos. 2,945,676, 2,945,677, 3,151,686,3,l58,206 and 3,158,208. In general, the devices illustrated thereinrely upon the maintenance of the predetermined fluid pressure in thecylinder and piston mechanism, while permitting relative telescopicmovement to occur between the cylinder and piston portions of themechanism.

Where the compensating apparatus is interposed between the travellingblock and hook, the available height or head room in a derrick isreduced. Derricks used on drilling vessels are designed to provide fornormal drilling operations; that is, to provide for the removal of andrunning-in of maximum lengths of drill pipes with respect to the wellbore. The length added between the travelling block and hook, such as inthe arrangement illustrated in US. Pat. No. 2,945,676, materiallylessens the available maximum travel of the drawworks or hoistingapparatus, requiring the raising and lowering of shorter strands ofdrill pipe in the well bore, which thereby increases the time requiredin making a round trip of the pipe in the well bore.

By virtue of the present invention, a compensating apparatus is sorelated to the travelling block and hook as to provide for a desirablemaximum stroke of the compensating apparatus, but in which the distanceadded by the compensating apparatus between the travelling block andhook is considerably reduced. As an example, only about one-half of theheight required with prior art devices is added with applicant'scombination of compensating apparatus supported between the travellingblock and a hook therebelow.

An object of the present invention is to provide ap paratus in which theheight added between the travelling block and hook is reducedconsiderablyby arranging the compensating apparatus in such manner thata substantial portion of its length straddles the travelling block andthe hook, thereby retaining a much greater derrick working height thanprovided by the mechanisms of the prior art.

The motion compensating apparatus is rendered inoperative during roundtripping of the drill pipe, or the like, the hook being mechanicallylocked to the travelling block permitting their joint movement in thesame manner as if the compensating apparatus were not present, therebyavoiding the necessity for retaining liquid under pressure in thecompensating apparatus. The locking together of the travelling block andhook, and their release from one another, can be effected from a remotepoint under the control of the operator. I

In the event'of sudden release or reduction of the load on thecompensating apparatus, the pressure therein would tend to drive thelower portion of the apparatus upwardly and create its impacting actionagainst other portions of the apparatus, with potential damage to theparts. I

A further objective of the present invention is to provide a safetyarrangement in which impact blows, orthe like, cannot occur, since theupward travel of the lower portion of the compensating device, in theevent of sudden reduction of the load thereon, is comparativelygradually arrested.

This invention possesses many other advantages, and has other objectswhich may be made more clearly ap parent from a consideration of a formin which it may be embodied. This form is shown in the drawingsaccompanying and forming part of the present specification. It will nowbe described in detail, for the purpose of illustrating the generalprinciples of the invention; but it is to be understood that suchdetailed description is not to be taken in a limiting sense.

Referring to the drawings:

FIG. 1 is a diagrammatic view. of an apparatus embodying the inventionin association with a rig mounted on a floating vessel for drilling awell bore underlying a body of water;

FIG. 2 is an isometric projection of a compensating apparatus inassociation with a travelling block and hook, the compensating apparatusbeing in its extended position;

FIG. 3 is an enlarged front elevational view, with parts shown inlongitudinal section, of the apparatus.

disclosed in FIG. 2 in a fully telescoped or collapsed position;

FIG. 4 is an enlarged longitudinal section through the An apparatus isillustrated in the drawings in connection with the drilling of avertical well bore W from a sub-aqueous floor F above which a drillingbarge B, or other floating vessel, is located, the barge being suitablyanchored against lateral displacement for the purpose of holding adrilling string S in centered relation with respect to the well bore. Adrill bit A is secured to the lower end of the drill string, such as astring of drill pipe or drill casing, the upper kelly portion K of thedrill string passing through the usual rotary table T rotated by asuitable drive mechanism (not shown). The upper end of the kelly issecured to a swivel C, which is, in turn, suspended from a hook Hpivotally connected to the lower portion of the compensating apparatusD, the upper portion of which is pivotally connected to a travellingblock E associated with the usual lines L passing over a crown block Mat the upper end of the derrick N mounted on the floating drillingvessel, the lines being connected to a suitable drawworks P mounted onthe vessel.

A mud line R is connected to the swivel for the purpose of pumpingdrilling mud, or the like, down the drill string S for discharge fromthe bit A for the purpose of removing the cuttings produced by thelatter, while the bit is rotated by the drill string an appropriatedrilling weight is imposed thereon. Usually, the drilling weight isprovided by a suitable length of drill collars disposed in the lowerportion of the drill string immediately above the drill bit, the drillstring above the drill collars being maintained in tension by thedrawworks P and lines L, the drawworks permitting the drill string tolower as the hole is cut by the bit.

The compensating apparatus D permits the floating vessel B, and themechanism carried thereby, to shift vertically relative to the well boreW without appreciably modifying the stress in the drill string S, and,therefore, the drilling weight imposed on the drill bit. Through themaintenance of fluid pressure in the compensating apparatus, the tensionor strain in the drill string is maintained substantially constant at aselected value, despite the heaving of the floating vessel in the bodyof water. The system for maintaining the desired pressure in thesupporting fluid in the compensating apparatus may be that disclosed inthe above United States patents. However, it is preferred to employ thesystem illustrated and described in the application of Edward Larraldeand Ronald E. Beaufort, for Hydraulic-Pneumatic Weight Control andCompensating Apparatus, Ser. No. 69,758, Filed Sept. 4, 1970. In generalthis latter system maintains the pressure of the liquid in the cylindersof the compensating apparatus at a selected constant value through useof an accumulator in which the pressure ofa gas 11 in an accumulator istransferred to a liquid medium 12 and to the portion of such liquidmedium disposed in the cylinders 13 of the compensating apparatus.

As specifically disclosed in the drawings, a pair of upper cylinders 13are disposed on opposite sides of the travelling block E, the upper ends14 of the cylinders terminating in substantially the same horizontalplane as contains the upper end of the travelling block. The lower endof each cylinder is connected to a base member 15 having opposedtrunnions 16 pivotally mounted in the lower ends of lower links 17straddling the cylinder, the upper ends of the links being connected bypins 18 to upper links 19, which, in turn, are

connected by pins 20 to an upper supporting structure or yoke 21 thatincludes spaced vertical members 22 maintained in parallel spacedrelation with respect to each other by being suitably secured tointervening 5 cross members or support plates 23 to 27. The lower endsportions of the sides of the travelling block E overlap the yoke members22, being pivotally secured thereto by a transverse pivot pin 28 passingthrough the upper portions of the yoke members 22 and the lower portionsof the travelling block.

A piston 29 is slidable in each cylinder, carrying suitable seal rings20 thereon for slidably sealing against the cylinder wall. The piston isconnected to the upper end of a piston rod 31 extending through the rodend 32 of the cylinder which carries a suitable side seal ring 33thereon for slidably sealing against the periphery of the rod. The lowerends of the rods depending from the cylinders straddle and are disposedon opposite sides of the hook H, being suitably secured to the lowerportions of a supporting structure 34, which also straddles the hook. Asspecifically disclosed, a collar 35 clamped around an upper collet 35aof a cross member 36 causes the collet to grip the lower portion of eachrod, a nut 37 being threaded on the rod and bearing against the lowerend of the cross member. The cross members are suitably secured tovertical plates 38, as through use of threaded fastening elements 39,which are attached to opposed upper members 40 of the supportingstructure 34 in any suitable manner, as through use of plates 41 andscrews 42, the opposed members having a supporting pin 43 extendingtherethrough which also passes through the upper end of the hook H,which is permitted to pivot about the axis of the supporting pin 43.

The tongue portion 44 of a releasable lock device, described more fullyhereinbelow, extends between the opposed members 40, being securedthereto in any suitably manner, as through use of threaded fasteningelements 45, the tongue extending above the upper ends of the opposedmembers 40 and having a hole 46 therethrough for reception of acompanion locking member 47 mounted on the upper supporting structure 21(FIG. 3), the upper end of the tongue being tapered to provide a guideor a nose 48.

It will be noted that the links l7, 19 on opposite sides of eachcylinder 13 are spaced transversely from one another, and that thevertical supporting portions 38, 41, 40 of the lower yoke structure 34are also spaced from one another, so as to permit maximum relativeelevation of the piston rods 31 within the cylinders 13 to the extent atwhich the upper ends of the opposed members 40 are disposed closelyadjacent to the lower ends of the side members 22 of the uppersupporting structure 21, and with the collets 35a disposed closelyadjacent to the bases 15 secured to the lower ends of the cylinders.With the parts in this relative position, the tongue 44 is disposedbetween a pair of lock receiver plates 24, 25, which also function ascross members secured to the opposed members 22 of the upper supportingstructure. One of these plates has a hole 50 alignable with the hole 46in the lock tongue, the other of the plates 24 and an outboard supportplate 23 carrying a support sleeve 51 in which a cylinder lock pin 47 isslidable, this cylinder being adapted to occupy a position in thesupport sleeve 51 fully retracted from the holes 46, 50 in the tongue 44and lock plate 25, or to be moved into such holes when they are alignedwith one another for the purpose of locking the lower supportingstructure 34 to the upper supporting structure 21 when the compensatorapparatus D is to be held ineffective and in a fully collapsed position,the bases being disposed adjacent to the collets 35a at this time, andwith the links 17 mounted within the side members 38, 41, 40 of thelower supporting structure.

The cylindrical lock pin 47 is slidable along a piston 53 receivedwithin an internal cylinder 54 of the lock pin, this piston beingsecured to a piston rod 55 projecting through a cylinder head 56threadedly secured to the lock pin 47, the other end of the rod beingthreadedly attached to the outer end of the' support sleeve 51. A hose57 is suitably connected to a pin retracting passage 58 in the pistonrod that communicates with an annular cylindrical space 59 between thepiston and the rod end 56 of the cylinder. Fluid under pressure can alsobe transmitted through a suitable hose 60 connected to a locking passage61 provided in the piston rod, which opens into the cylinder space 62forwardly of the piston, the outer end of this cylinder space beingclosed by a suitable plug or closure member 63. Leakage of fluid fromthese spaces 59, 62 is prevented by suitable seal rings 64 on the pistonslidably engaging the inner wall of the cylinder lock pin 47, and by asuitable rod packing 65 on the cylinder head 56 slidably and sealinglyengaging the periphery of the piston rod 55.

When fluid under pressure is introduced through the locking passage 61into the locking cylinder space 62, with the pin retracting passage 58being open to discharge of fluid from the retracting cavity 59, the lockpin is projected in a forward direction into both holes 46, 50 in thetongue 44 and the lock plate 25, thereby locking the lower supportingstructure 34 to the upper supporting structure 21, and retaining thecompensating apparatus in its fully telescoped or collapsed position. Onthe other hand, the relieving of the pressure in the locking passage 62and the introduction of pressure through the retracting passage 58 intothe annular cavity 59 will cause the cylindrical lock pin 47 to beretracted completely from the holes 50, 46, thereby allowing removal ofthe tongue 44 with respect to the receiver lock plates 24, 25, and thelowering of the hook H with respect to the travelling block E.

As described in the above patent application of Edward Larralde andRonald E.'Beaufort, liquid under pressure is present in the annularcylinder space 70 around each piston rod 31, exerting an upward liftingforce on the pistons 29 and the rods 31. The desired pressure in theliquid is maintained by an accumulator arrangement 10 in which asuitable gas 11 under pressure will exert its pressure force through afloating piston 71 on the liquid 12 in the system (FIG. 1). Heaving ofthe vessel B can take place without inducing corresponding motion in therunning string S supported from the hook H, inasmuch as the entire rig,with the crown block M, lines L, travelling block E and cylinders 13move vertically with respect to the drill string, the appropriatetension in the drill string being maintained. Relative tilting betweenthe compensating apparatus D and hook H can take place about the axis ofthe hinge pin 43. Tilting can also take place about the axis of thetransverse pivot pin 28 pivotally securing the upper structure 21 to thetravelling block E. In this connection, the links 17, 19 and the pinconnections 16, 18, 20 therebetween and with the cylinders 13 and upperstructure 21 permit the relative tilting action to. occur between thecompensating apparatus D and the travelling block E and hook H.

It is to be noted that the upper portions of the cylinders 13 extend onopposite sides of the travelling block E, terminating substantially inthe horizontal plane of the upper end of the travelling block.Similarly, the piston rods 31 and the lower supporting structure 34extend downwardly along a substantial length of the hook H. In addition,the ability of the links 17, 19 to nest between the sides 38, 41, 40 ofthe lower supporting structure, when the compensating apparatus is in afully collapsed position, and with the pistons 29 at the upper ends ofthe cylinders 13, decreases considerably the overall collapsed height ofthe apparatus, adding only a few feet to the total distance between thelower end of the hook H and the upper end of the travelling block E, ascompared with conventional apparatus in which the hook H is pivotallyconnected directly to the travelling block. The relationship of parts,by adding only a short length to the overall length of the apparatus,permits standard types of derricks N to be used and the usual maximumlength of drill pipe, and the like, to be raised and lowered in thederrick. This is to be distinguished with the mounting of a singlecylinder 13, and piston 29 and rod 31 between the travelling block andhook and in alignment therewith, as in the prior art, which would limitthe total length of pipe that could be elevated in a standard derrick,or which would require the use of derricks of additional height, ascompared with the heights of derricks presently being used.

The present arrangement not only shortens considerably the overallheight of the apparatus D when in the collapsed position, but it alsodecreases the head room required above the travelling block during theoperation of the compensator apparatus. If a single cylinder, piston andpiston rod were used, in alignment with the travelling block and hook,the additional head room required would be more than twice the stroke ofthe unit. However, by virtue of the present straddling relationshipbetween the cylinders 13 and travelling block E, and of the lowerportions of the piston rods 31 with respect to the hook H, only aboutone-half of the additional head room is required, and this addedrequirement of head room is already provided for in the standard heightsof derricks. In addition, through avoiding the necessity of providingderricks of extra height, the center of gravity of the derrick ismaintained at a lower point, which is of importance with a derrickmounted on a floating vessel.

The apparatus D can be locked in its fully retracted or collapsedposition when the drill pipe is to be round tripped, or when it isdesirable for the motion compensating apparatus to be held ininoperative condition.

Such locking can take place upon relatively lowering the travellingblock E toward the hook H, so that the cylinders 13 shift downwardlyalong the pistons 29 and piston rods 31 to the fully collapsed position,the locking tongue 44 being disposed between the receiver plates 24, 25with the tongue hole 46 in alignment with the cylinder lock pin 47 andthe companion hole 50 in the receiver lock plate 25. Fluid underpressure is then introduced through the locking passage 61 into thecylinder space 62 forwardly of the piston 53 to shift the pin 47 throughthe holes 46, 50 to its fullest extent, as illustrated in FIGS. 3 and 4.The pin 47 will remain in that condition. The rig is now in condition tobe used for round tripping, or the like, in the same manner as if thecompensating portion D of the apparatus were absent.

When the compensating apparatus is to be permitted to function, thefluid pressure in the locking passage 61 and cylinder cavity 62 isrelieved, and fluid under pressure introduced through the retractingpassage 58 into the annular cavity 59, thereby effecting shifting of thelock pin 47 to its fully retracted position, in which it has beencompletely withdrawn from the holes 50, 46 in the receiver lock plate 25and tongue 44, whereupon the travelling block E and hook H can movevertically with respect to each other, the cylinders 13 shiftinglongitudinally with respect to the pistons 29 and piston rods 31.

In the event of a sudden reduction in the load on the travelling hook E,as through a twist off, or other failure, of the drill pipe S, the fluid12 under pressure tends to drive the pistons 29 and rods 31 upwardly ina comparatively rapid manner, which could cause an impacting of theparts upon one another, such as an impacting of the collets 35a on thebases of the cylinder supporting structures. Such sudden shifting andpotential damage to the apparatus is prevented by the provision ofvelocity sensitive shock absorbers 80 i that can operate between theupper and lower supporting structures 21, 34. Each of these shockabsorbers includes an upper cylinder head 81 secured by screws 82, orthe like, to a cross plate 27 suitably attached to the side members 22of the upper structure 21, an elongate cylinder sleeve 83 beingthreadedly secured to this head and extending downwardly therefrom. Alower head 84 is threadedly secured to this sleeve 83, this lower headhaving a suitable packing 85 slidably sealing against a piston rod 86extending therethrough and upwardly into the cylinder sleeve, the upperend of the rod being suitably attached to a piston 87 having a packing88 thereon for slidably sealing against the wall of the cylinder sleeve83. This piston has one or a plurality of orifices 89 extendingtherethrough an interconnecting the cylinder space 90 above the pistonwith the annular cylinder space 91 below the piston. The cylinder iscompletely filled with oil, or other suitable liquid, both above andbelow the piston 87.

Normally, gravity will pull each piston rod 86 and piston 87 downwardly,the liquid in the lower cylinder space 91 transferring in a relativelyslow manner through the orifices 89 to the cylinder space 90 above thepiston. Accordingly, during the normal operation of the compensatorapparatus, the piston 87 is disposed in the lower portion of thecylinder 83, with the piston rod 86 depending downwardly to asubstantial extent below the lower cylinder head 84, there being animpact head 93 threadedly attached to the lower end of the piston rod.

An actuating cross plate 94 is secured to the side members 40 of thelower structure 34 in alignment with each piston rod 86, this actuatingplate having an upwardly opening recess 95 therein of a diameter toreceive the impact head 93.

Assuming the shock absorbing pistons 87 and piston rods 86 are in theirlower position within the shock absorber cylinders 83, and thecompensating apparatus D in its normal operating condition in whichrelative vertical movement can occur between the travelling block E andhook H, as well as between the compensator cylinders 13, on the onehand, and pistons 29 and piston rods 31, on the other hand, the shockabsorbers 83 play no part in the operation of the apparatus. However, inthe event the load on the hook H is suddenly reduced, the compensatingpistons 29 and rods 31 retract upwardly suddenly. Such upward movementis decelerated and brought to a relatively gradual stop by theengagement of the actuating plates 94 with the impact heads 93,resulting in the piston rods 86 and the pistons 87 connected theretobeing urged upwardly in the shock absorber cylinders 83. However, therate of upward movement of the lower supporting structure 34 and of therods 86 and pistons 87 is retarded by the necessity of the liquid in theshock absorber cylinders above the pistons 87 to transfer through theflow restricting orifices 89 into the cylinder spaces 91 below thepistons 87, time being required for each liquid transfer to take place,thereby gradually bringing the lower supporting structure 34 and thepistons 29 and piston rods 31 connected thereto to a full stop, whichwill occur when the compensating apparatus D is disposed in its fullycollapsed position. Thus, the velocity sensitive shock absorbersfunction to decelerate movement of the lower portion of the apparatuswith respect to the upper portion, preventing the parts from impactingwith high energy upon one another.

When the compensating apparatus is again to be placed in an operativecondition, relative lowering of the lower structure 34, piston rods 31and pistons 29 relative to the compensator cylinders 13 and upperstructure 21 can take place without restraint, the lowering of theactuating plates 94 with respect to the shock absorber impacting heads93 and rods 86 allowing the shock absorber rods 86 and pistons 87 togradually descend in the shock absorber cylinders 83 to their lowermostposition, in which they can again be effective to decelerate the upwardmovement of the lower portions of the compensator relative to the upperportions.

We claim:

1. In apparatus for maintaining a predetermined stress in a runningstring supported by a rig mounted on a vessel floating in a body ofwater: a motion compensator apparatus for maintaining the running stringin substantially a predetermined position as the vessel heaves in thebody of water, comprising an upper support carried by said rig, a lowersupport connectible to the running string, a plurality of cylindermeans, a plurality of piston means slidable in said plurality ofcylinder means, one of said plurality of means being connectible to oneof said supports, the other of said plurality of means straddling andbeing connected to the other of said supports, and means for maintaininga fluid medium under pressure in said plurality of cylinder means on oneside of said plurality of piston means as said plurality of piston meansand plurality of cylinder means move longitudinally relative to oneanother in both longitudinal directions in response to heaving of saidvessel in the body of water.

2. In apparatus as defined in claim 1; said one of said plurality ofmeans straddling said one of said supports.

3. In apparatus as defined in claim 1; said one of said plurality ofmeans being connected to said lower support; said other of saidplurality of means being connected to said upper support.

4. In apparatus as defined in claim 1; said one of said plurality ofmeans being connected to said lower support; said other of saidplurality of means being connected to said upper support; said one ofsaid plurality of means straddling said lower support.

5. In apparatus for maintaining a predetermined stress in a runningstring: a first support; a second support connectible to the runningstring; a plurality of cylinder means; a plurality of piston meansslidable in said plurality of cylinder means; one of said plurality ofmeans being connected to one of said supports; the other of saidplurality of means straddling and being connected to the other of saidsupports; and means for maintaining a fluid medium under pressure insaid plurality of cylinder means on one side of said plurality of pistonmeans as said plurality of piston means and plurality of cylinder meansmove longitudinally relative to one another in both longitudinaldirections; and means for releasably locking said supports to each otherto prevent relative longitudinal movement between said plurality ofcylinder means and plurality of piston means.

6. In apparatus for maintaining a predetermined stress in a runningstring: a first support; a second support connectible to the runningstring; a plurality of cylinder means; a plurality of piston meansslidable in said plurality of cylinder means; one of said plurality ofmeans being connected to one of said supports; the other of saidplurality of means straddling and being connected to the other of saidsupports; and means for maintaining a fluid medium under pressure insaid plurality of cylinder means on one side of said plurality of pistonmeans as said plurality of piston means and plurality of cylinder meansmove longitudinally relative to one another in both longitudinaldirections; said one of said plurality of means being connected to saidsecond support; said other of said plurality of means being connected tosaid first support; and means for releasably locking said supportstoeach other when said plurality of piston means are fully telescopedwithin said plurality of cylinder means to prevent relative longitudinalmovement between said plurality of cylinder means and plurality ofpiston means.

7. In apparatus as defined in claim 6; means for decelerating relativelongitudinal movement between said plurality of cylinder means andplurality of piston means upon substantial reduction in the stress inthe running string; said decelerating means being disposed substantiallyparallel to and between at least one of said plurality of means.

8. In apparatus for maintaining a predetermined stress in a runningstring: a first support; a second support connectible to the runningstring; a plurality of cylinder means; a plurality of piston meansslidable in said plurality of cylinder means; one of said plurality ofmeans being connected to one of said supports; the other of saidplurality of means straddling and being connected to the other of saidsupports; and means for maintaining a fluid medium under pressure insaid plurality of cylinder means on one side of said plurality of pistonmeans as said plurality of piston means and plurality of cylinder meansmove longitudinally relative to one another in both longitudinaldirections; and means for decelerating relative longitudinal movementbetween said plurality of cylinder means and plurality of pistonmeansupon substantial reduction in the stress in the running string.

9. In apparatus as defined in claim 8; said decelerating means beingdisposed substantially parallel to and between at least one of saidplurality of means. 7

10. In apparatus for maintaining a predetermined stress in a runningstring disposed in a well bore and which is supported by a rig,including a derrick and a suspension mechanism supported from the upperportion of the derrick: ,a travelling block adapted to form part of thesuspension mechanism; a hook adapted to support the running stringtherebelow; a motion compensating apparatus between and connected tosaid block and hook, said motion compensating apparatus comprising anupper support connected to said travelling block, a lower supportconnected to said hook; a plurality of cylinder means carried by one ofsaid supports and straddling said travelling block or hook; a pluralityof piston means slidable in said cylinder means and carried by saidother of said supports; and means for maintaining a fluid medium underpressure in said plurality of cylinder means on one side of saidplurality of piston means as said plurality of piston means andplurality of cylinder means move longitudinally relative to one anotherin both longitudinal directions.

11. In apparatus as defined in claim 10; said plurality of cylindermeans being carried by said upper support, extending upwardly therefrom,and straddling said travelling block, said plurality of piston meansbeing carried by said lower support.

12. In apparatus as defined in claim 10; said plurality of cylindermeans being carried by said upper support, extending upwardly therefrom,and straddling said travelling block, said plurality of piston meansbeing carried by said lower support and straddling said lower support,the lower portion of said plurality of cylinder means moving into aposition straddling said lower support when said plurality of pistonmeans are telescoped substantially fully within said plurality ofcylinder means. 7

13. In apparatus as defined in claim 10; said plurality of cylindermeans being carried by said upper support, extending upwardly therefrom,and straddling said travelling block, said plurality of piston meansbeing carried by said lower support and straddling said lower supportand hook, the lower portion of said plurality of cylinder means movinginto a position straddling said lower support and book when saidplurality of piston means are telescoped substantially fully within saidplurality of cylinder means.

14. In apparatus as defined in claim 10; and means for releasablylocking said supports to each other to prevent relative longitudinalmovement between said plurality of cylinders means and plurality ofpiston means.

15. In apparatus as defined in claim said plurality of cylinder meansbeing carried by said upper support, extending upwardly therefrom, andstraddling said travelling block, said plurality of piston means beingcarried by said lower support; and means for releasably locking saidsupports to each other when said plurality of piston means aresubstantially fully telescoped within said plurality of cylinder meansto prevent relative longitudinal movement between said plurality ofcylinder means and plurality of piston means.

16. In apparatus as defined in claim 10; said plurality of cylindermeans being carried by said upper support, extending upwardly therefrom,and straddling said travelling block, said plurality of piston meansbeing carried by said lower support and straddling said lower support,the lower portion of said plurality of cylinder means moving into aposition straddling said lower support when said plurality of pistonmeans are telescoped substantially fully within said plurality ofcylinder means; and means for releasably locking said supports to eachother when said plurality of piston means are substantially fullytelescoped within said plurality of cylinder means to prevent relativelongitudinal movement between said plurality of cylinder means andplurality of piston means.

17. In apparatus as defined in claim 10; said plurality of cylindermeans being carried by said upper support, extending upwardly therefrom,and straddling said travelling block, said plurality of piston meansbeing carried by said lower support and straddling said lower supportand hook, the lower portion of said plurality of cylinder means movinginto a position straddling said lower support and hook when saidplurality of piston means are telescoped substantially fully within saidplurality of cylinder means; and means for releasably locking saidsupports to each other when said plurality of piston means aresubstantially fully telescoped within said plurality of cylinder meansto prevent relative longitudinal movement between said plurality ofcylinder means and plurality of piston means.

18. In apparatus as defined in claim 10; and means for deceleratingrelative longitudinal movement between said plurality of cylinder meansand plurality of piston means upon substantial reduction in the stressin the running string.

19. In apparatus as defined in claim 10; said plurality of cylindermeans being carried by said upper support, extending upwardly therefrom,and straddling said travelling block, said plurality of piston meansbeing carried by said lower support; and means for decelerating relativelongitudinal movement between said plurality of cylinder means andplurality of piston means upon substantial reduction in the stress inthe running string; said decelerating means being carried by said uppersupport, depending therefrom, and being disposed parallel to and betweensaid plurality of cylinder means moving into a position straddling saidlower support and hook when said plurality of piston relativelongitudinal movement between said plurality of cylinder means andplurality of piston means upon substantial reduction in the stress inthe running string; said decelerating means being carried by said uppersupport, depending therefrom, and being disposed parallel to and betweensaid plurality of cylinder means.

21. In apparatus for maintaining a predetermined stress in a runningstring disposed in a well bore and which is supported by a rig,including a derrick and a suspension mechanism supported from the upperportion of the derrick: a travelling block structure adapted to formpart of the suspension mechanism; a hook structure adapted to supportthe running string therebelow; a motion compensating apparatuscomprising cylinder means connected to and in overlapping relation toone of said structures, piston means connected to the other of saidstructures and slidable relatively in said cylinder means; and means formaintaining a fluid medium under pressure in said cylinder means on oneside of said piston means as said piston means and cylinder means movelongitudinally relatiye to one another in both longitudinal directions,whereby the predetermined stress in the running string is maintained.

22. In apparatus as defined in claim 21; said cylinder means beingconnected to and in overlapping relation to said travelling blockstructure; said piston means being connected to said hook structure.

23. In apparatus as defined in claim 21; and means for releasablylocking said cylinder means and piston means to each other when saidpiston means is substantially fully telescoped within said cylindermeans to prevent relative longitudinal movement between said cylindermeans and piston means.

24. In apparatus as defined in claim 21; said cylinder means beingconnected to and in overlapping relation to said travelling blockstructure; said piston means being connected to said hook structure; andmeans for releasably locking said cylinder means and piston means toeach other when said piston means is substantially fully telescopedwithin said cylinder means to prevent relative longitudinal movementbetween said cylinder means and piston means.

1. In apparatus for maintaining a predetermined stress in a runningstring supported by a rig mounted on a vessel floating in a body ofwater: a motion compensator apparatus for maintaining the running stringin substantially a predetermined position as the vessel heaves in thebody of water, comprising an upper support carried by said rig, a lowersupport connectible to the running string, a plurality of cylindermeans, a plurality of piston means slidable in said plurality ofcylinder means, one of said plurality of means being connectible to oneof said supports, the other of said plurality of means straddling andbeing connected to the other of said supports, and means for maintaininga fluid medium under pressure in said plurality of cylinder means on oneside of said plurality of piston means as said plurality of piston meansand plurality of cylinder means move longitudinally relative to oneanother in both longitudinal directions in response to heaving of saidvessel in the body of water.
 1. In apparatus for maintaining apredetermined stress in a running string supported by a rig mounted on avessel floating in a body of water: a motion compensator apparatus formaintaining the running string in substantially a predetermined positionas the vessel heaves in the body of water, comprising an upper supportcarried by said rig, a lower support connectible to the running string,a plurality of cylinder means, a plurality of piston means slidable insaid plurality of cylinder means, one of said plurality of means beingconnectible to one of said supports, the other of said plurality ofmeans straddling and being connected to the other of said supports, andmeans for maintaining a fluid medium under pressure in said plurality ofcylinder means on one side of said plurality of piston means as saidplurality of piston means and plurality of cylinder means movelongitudinally relative to one another in both longitudinal directionsin response to heaving of said vessel in the body of water.
 2. Inapparatus as defined in claim 1; said one of said plurality of meansstraddling said one of said supports.
 3. In apparatus as defined inclaim 1; said one of said plurality of means being connected to saidlower support; said other of said plurality of means being connected tosaid upper support.
 4. In apparatus as defined in claim 1; said one ofsaid plurality of means being connected to said lower support; saidother of said plurality of means being connected to said upper support;said one of said plurality of means straddling said lower support.
 5. Inapparatus for maintaining a predetermined stress in a running string: afirst support; a second support connectible to the running string; aplurality of cylinder means; a plurality of piston means slidable insaid plurality of cylinder means; one of said plurality of means beingconnected to one of said supports; the other of said plurality of meansstraddling and being connected to the other of said supports; and meansfor maintaining a fluid medium under pressure in said plurality ofcylinder means on one side of said plurality of piston means as saidplurality of piston means and plurality of cylinder means movelongitudinally relative to one another in both longitudinal directions;and means for releasably locking said supports to each other to preventrelative longitudinal movement between said plurality of cylinder meansand plurality of piston means.
 6. In apparatus for maintaining apredetermined stress in a running string: a first support; a secondsupport connectible to the running string; a plurality of cylindermeans; a plurality of piston means slidable in said plurality ofcylinder means; one of said plurality of means being connected to one ofsaid supports; the other of said plurality of means straddling and beingconnected to the other of said supports; and means for maintaining afluid medium under pressure in said plurality of cylinder means on oneside of said plurality of piston means as said plurality of piston meansand plurality of cylinder means move longitudinally relative to oneanother in both longitudinal directions; said one of said plurality ofmeans being connected to said second support; said other of saidplurality of means being connected to said first support; and means forreleasably locking said supports to each other when said plurality ofpiston means are fully telescoped within said plurality of cylindermeans to prevent relative longitudinal movement between said pluralityof cylinder means and plurality of piston means.
 7. In apparatus asdefined in claim 6; means for decelerating relative longitudinalmovement between said plurality of cylinder means and plurality ofpiston means upon substantial reduction in the stress in the runningstring; said decelerating means being disposed substantially parallel toand between at least one of said plurality of means.
 8. In apparatus formaintaining a predetermined sTress in a running string: a first support;a second support connectible to the running string; a plurality ofcylinder means; a plurality of piston means slidable in said pluralityof cylinder means; one of said plurality of means being connected to oneof said supports; the other of said plurality of means straddling andbeing connected to the other of said supports; and means for maintaininga fluid medium under pressure in said plurality of cylinder means on oneside of said plurality of piston means as said plurality of piston meansand plurality of cylinder means move longitudinally relative to oneanother in both longitudinal directions; and means for deceleratingrelative longitudinal movement between said plurality of cylinder meansand plurality of piston means upon substantial reduction in the stressin the running string.
 9. In apparatus as defined in claim 8; saiddecelerating means being disposed substantially parallel to and betweenat least one of said plurality of means.
 10. In apparatus formaintaining a predetermined stress in a running string disposed in awell bore and which is supported by a rig, including a derrick and asuspension mechanism supported from the upper portion of the derrick: atravelling block adapted to form part of the suspension mechanism; ahook adapted to support the running string therebelow; a motioncompensating apparatus between and connected to said block and hook,said motion compensating apparatus comprising an upper support connectedto said travelling block, a lower support connected to said hook; aplurality of cylinder means carried by one of said supports andstraddling said travelling block or hook; a plurality of piston meansslidable in said cylinder means and carried by said other of saidsupports; and means for maintaining a fluid medium under pressure insaid plurality of cylinder means on one side of said plurality of pistonmeans as said plurality of piston means and plurality of cylinder meansmove longitudinally relative to one another in both longitudinaldirections.
 11. In apparatus as defined in claim 10; said plurality ofcylinder means being carried by said upper support, extending upwardlytherefrom, and straddling said travelling block, said plurality ofpiston means being carried by said lower support.
 12. In apparatus asdefined in claim 10; said plurality of cylinder means being carried bysaid upper support, extending upwardly therefrom, and straddling saidtravelling block, said plurality of piston means being carried by saidlower support and straddling said lower support, the lower portion ofsaid plurality of cylinder means moving into a position straddling saidlower support when said plurality of piston means are telescopedsubstantially fully within said plurality of cylinder means.
 13. Inapparatus as defined in claim 10; said plurality of cylinder means beingcarried by said upper support, extending upwardly therefrom, andstraddling said travelling block, said plurality of piston means beingcarried by said lower support and straddling said lower support andhook, the lower portion of said plurality of cylinder means moving intoa position straddling said lower support and hook when said plurality ofpiston means are telescoped substantially fully within said plurality ofcylinder means.
 14. In apparatus as defined in claim 10; and means forreleasably locking said supports to each other to prevent relativelongitudinal movement between said plurality of cylinders means andplurality of piston means.
 15. In apparatus as defined in claim 10; saidplurality of cylinder means being carried by said upper support,extending upwardly therefrom, and straddling said travelling block, saidplurality of piston means being carried by said lower support; and meansfor releasably locking said supports to each other when said pluralityof piston means are substantially fully telescoped within said pluralityof cylinder means to prevent relative longitudinal movement between saidplurAlity of cylinder means and plurality of piston means.
 16. Inapparatus as defined in claim 10; said plurality of cylinder means beingcarried by said upper support, extending upwardly therefrom, andstraddling said travelling block, said plurality of piston means beingcarried by said lower support and straddling said lower support, thelower portion of said plurality of cylinder means moving into a positionstraddling said lower support when said plurality of piston means aretelescoped substantially fully within said plurality of cylinder means;and means for releasably locking said supports to each other when saidplurality of piston means are substantially fully telescoped within saidplurality of cylinder means to prevent relative longitudinal movementbetween said plurality of cylinder means and plurality of piston means.17. In apparatus as defined in claim 10; said plurality of cylindermeans being carried by said upper support, extending upwardly therefrom,and straddling said travelling block, said plurality of piston meansbeing carried by said lower support and straddling said lower supportand hook, the lower portion of said plurality of cylinder means movinginto a position straddling said lower support and hook when saidplurality of piston means are telescoped substantially fully within saidplurality of cylinder means; and means for releasably locking saidsupports to each other when said plurality of piston means aresubstantially fully telescoped within said plurality of cylinder meansto prevent relative longitudinal movement between said plurality ofcylinder means and plurality of piston means.
 18. In apparatus asdefined in claim 10; and means for decelerating relative longitudinalmovement between said plurality of cylinder means and plurality ofpiston means upon substantial reduction in the stress in the runningstring.
 19. In apparatus as defined in claim 10; said plurality ofcylinder means being carried by said upper support, extending upwardlytherefrom, and straddling said travelling block, said plurality ofpiston means being carried by said lower support; and means fordecelerating relative longitudinal movement between said plurality ofcylinder means and plurality of piston means upon substantial reductionin the stress in the running string; said decelerating means beingcarried by said upper support, depending therefrom, and being disposedparallel to and between said plurality of cylinder means.
 20. Inapparatus as defined in claim 10; said plurality of cylinder means beingcarried by said upper support, extending upwardly therefrom, andstraddling said travelling block, said plurality of piston means beingcarried by said lower support and straddling said lower support andhook, the lower portion of said plurality of cylinder means moving intoa position straddling said lower support and hook when said plurality ofpiston means are telescoped substantially fully within said plurality ofcylinder means; and means for decelerating relative longitudinalmovement between said plurality of cylinder means and plurality ofpiston means upon substantial reduction in the stress in the runningstring; said decelerating means being carried by said upper support,depending therefrom, and being disposed parallel to and between saidplurality of cylinder means.
 21. In apparatus for maintaining apredetermined stress in a running string disposed in a well bore andwhich is supported by a rig, including a derrick and a suspensionmechanism supported from the upper portion of the derrick: a travellingblock structure adapted to form part of the suspension mechanism; a hookstructure adapted to support the running string therebelow; a motioncompensating apparatus comprising cylinder means connected to and inoverlapping relation to one of said structures, piston means connectedto the other of said structures and slidable relatively in said cylindermeans; and means for maintaining a fluid medium under pressure in saidcylinder means on one Side of said piston means as said piston means andcylinder means move longitudinally relative to one another in bothlongitudinal directions, whereby the predetermined stress in the runningstring is maintained.
 22. In apparatus as defined in claim 21; saidcylinder means being connected to and in overlapping relation to saidtravelling block structure; said piston means being connected to saidhook structure.
 23. In apparatus as defined in claim 21; and means forreleasably locking said cylinder means and piston means to each otherwhen said piston means is substantially fully telescoped within saidcylinder means to prevent relative longitudinal movement between saidcylinder means and piston means.